The bandwidth requirements of modern and future automotive applications are posing a relevant challenge to current in-vehicle networking (IVN) technologies such as Controller Area Network (CAN) and FlexRay™. Thanks to the latest development of the Ethernet technology, a 100 Mbps Ethernet link can now be implemented on an unshielded twisted pair of copper wires while limiting the EMI emissions below the threshold imposed by the regulatory automotive standards.
Ethernet is a point to point communication technology. More complex networks are created by using layer 2 (according to the ISO/OSI stack) bridges (also called switches). Switches enable the definition of complex network topologies and offer many services including the basic relying of frames (the basic Ethernet communication element) from one source node to multiple destinations, and more complex operations such as channel bandwidth allocation, network partitioning via virtual LANs (VLANs) and traffic prioritization. Switched Ethernet networks have been implemented in the automotive market for supporting bandwidth-intensive applications such as infotainment and surround-view applications. These applications make use of audio and video streams that are generated by a single source, also called Talker (e.g., a camera or multimedia player) and distributed to one or more Listeners (e.g., head unit or remote screens and audio amplifiers). To optimize the handling of these data streams the IEEE has defined Audio/Video Broadcasting (AVB) standards that allows switches to identify different types of traffic streams and categorize them into different traffic classes.
The IEEE standards define a collection of standards targeted to optimize the transmission of audio and video streams on an Ethernet network under the name of AVB (Audio/Video Broadcasting). The main standards relevant for this work are the following:
802.1Qat—Stream reservation protocol: is a distributed protocol that allows talkers to advertise available streams and listeners to register to a selected stream and reserve the necessary bandwidth in the relevant switches;
802.1Qav—Forwarding and Queuing Enhancements for Time-Sensitive Streams: defines a Credit Shaper hardware component capable of allocating specific amounts of bandwidth to a traffic class identified by a traffic priority;
802.1AS—Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks: specifies the protocol to be implemented by all end-nodes (e.g. ECUs) and switches of a network so that all the nodes of the network remain synchronized;
802.1BA—Audio Video Bridging (AVB) Systems: defines the AVB profile, in terms of configuration and features of the previous standards that all AVB systems should have.
These standards/protocols are implemented by network nodes including network switches. IEEE 802.1Q defines traffic Class A as a class whose streams generate one or more frames every 125 μs while Class B has a period of 250 us. The size of each frame depends on the specific format of the stream being transmitted.
Ethernet based networking has already been adopted by the automotive industry. The industry is now considering the adoption of Ethernet for safety-critical applications and has created the AVNU/AAA2C committee. The goal of this committee is to define a set of requirements to be adopted into a revised version of the IEEE AVB standards. The future version of AVB will be called Time-Sensitive Networks (TSN). An important element of AVB and TSN is the distributed synchronization protocol (IEEE 802.1AS) that allows all nodes of the network and the switches to share a common time reference with minimal jitter. This aspect enables lip sync reproduction of audio and video streams on different end points but also the correct fusion of data coming from different sensors such as cameras and radars.